Typical problems associated with transmitting compressed video over wireless networks include Quality of Service (QoS), latency and maintaining basic image integrity. For example, if a single packet of transmitted video data is lost, the fact that the video data is typically compressed in the temporal domain can cause propagation and cascading of a single artifact in one frame through multiple successive frames. Such lossy wireless networks may operate wireless protocols, such as those described by IEEE 802.11x and 802.15.3a, and video compression algorithms such as those described by the AVC video standard. Lossy networks may use transmission methods other than wireless such as, for example, HomePlug AV Powerline Communications.
During video transmission over a lossy network, video data (sometimes referred to as “video packets”) may be lost. For example, wireless lossy transmission mediums can be unreliable in that the transmitted video packets may not always be received (accurately or at all) by the wireless receiver. To counter this, the 802.11x Media Access Control (MAC) requires that in most cases a packet (or group of packets for 802.11e extensions to the standard) that is received will be acknowledged to the transmitter by sending back an “ACK” signal. Hence a missing ACK signal normally indicates that a video packet (or packets) has been lost.
In addition, video packet data can also be lost at the receiver. For example, as Advanced Video Coding (AVC) encoded data tends to be bursty, an unexpectedly large burst can overflow buffers on the receiver-side at several locations between the 802.11x module and the AVC decoder itself. Most packets lost in this way can be detected by Real-Time Transport Protocol (RTP) feedback.
To alleviate some of the inherent drawbacks associated with lossy network communication, various data recovery and error correction features have been built into the data coding standard used. For example, H264/AVC is a more recently developed coding standard which includes a Video Coding Layer (VCL) to efficiently represent the video content, and a Network Abstraction Layer (NAL) to format the VCL representation of the video and provide header information in a manner appropriate for conveyance by particular transport layers or storage media. Despite these efforts, there is a need to improve transmission reliability and error concealment over lossy network connections, such as 802.11x networks.
Thus, there is still an unsatisfied need for an improved system and method for transmitting video data over networks in a manner which decreases the probability of a failed transmission, improves the probability of successful decoding and/or increases the quality of error concealment on the receiver-side.